page_title: Calutron
section_title: Research
hierarchical_section_title: Calutron / Research
caption_attribution_description: English: Located in Building 9731 with a two bin Beta development unit, this calutron was used for research, development and training
context_page_description: A calutron is a mass spectrometer originally designed and used for separating the isotopes of uranium. It was developed by Ernest Lawrence during the Manhattan Project and was based on his earlier invention, the cyclotron. Its name was derived from California University Cyclotron, in tribute to Lawrence's institution, the University of California, where it was invented. Calutrons were used in the industrial-scale Y-12 uranium enrichment plant at the Clinton Engineer Works in Oak Ridge, Tennessee. The enriched uranium produced was used in the Little Boy atomic bomb that was detonated over Hiroshima on 6 August 1945.
  The calutron is a type of sector mass spectrometer, an instrument in which a sample is ionized and then accelerated by electric fields and deflected by magnetic fields. The ions ultimately collide with a plate and produce a measurable electric current. Since the ions of the different isotopes have the same electric charge but different masses, the heavier isotopes are deflected less by the magnetic field, causing the beam of particles to separate into several beams by mass, striking the plate at different locations.
context_section_description: While the process had been demonstrated to work, considerable effort was still required before a prototype could be tested in the field. Lawrence assembled a team of physicists to tackle the problems, including David Bohm, Edward Condon, Donald Cooksey, A. Theodore Forrester, Irving Langmuir, Kenneth Ross MacKenzie, Frank Oppenheimer, J. Robert Oppenheimer, William E. Parkins, Bernard Peters and Joseph Slepian. In November 1943 they were joined by a British Mission headed by Oliphant that included fellow Australian physicists Harrie Massey and Eric Burhop, and British physicists such as Joan Curran and Thomas Allibone.
  Lawrence had a large cyclotron under construction at Berkeley, one with a 184-inch (470 cm) magnet. This was converted into a calutron that was switched on for the first time on 26 May 1942. Like the 37-inch version, it looked like a giant C when viewed from above. The operator sat in the open end, whence the temperature could be regulated, the position of the electrodes adjusted, and even components replaced through an airlock while it was running. The new, more powerful calutron was not used to produce enriched uranium, but for experiments with multiple ion sources. This meant having more collectors, but it multiplied the throughput.
  The problem was that the beams interfered with each other, producing a series of oscillations called hash. An arrangement was devised that minimized the interference, resulting in reasonably good beams being produced, in September 1942. Robert Oppenheimer and Stan Frankel invented the magnetic shim, a device used to adjust the homogeneity of a magnetic field. These were sheets of iron about 3 feet (1 m) in width that were bolted to the top and bottom of the vacuum tank. The effect of the shims was to slightly increase the magnetic field in such a way as to help focus the ion beam. Work would continue on the shims through 1943. The main calutron patents were Methods of and apparatus for separating materials (Lawrence), Magnetic shims (Oppenheimer and Frankel), and Calutron system (Lawrence).
  Burhop and Bohm later studied the characteristics of electric discharges in magnetic fields, today known as Bohm diffusion. Their papers on the properties of plasmas under magnetic containment would find usage in the post-war world in research into controlled nuclear fusion. Other technical problems were more mundane but no less important. Although the beams had low intensity, they could, over many hours of operation, still melt the collectors. A water cooling system was therefore added to the collectors and the tank liner. Procedures were developed for cleaning the "gunk" that condensed inside the vacuum tank. A particular problem was blockage of the slits by "crud", which caused the ion beams to lose focus, or stop entirely.
  The chemists had to find a way of producing quantities of uranium tetrachloride (UCl
  ₄) from uranium oxide. (Nier had used uranium bromide.) Initially, they produced it by using hydrogen to reduce uranium trioxide (UO
  ₃) to uranium dioxide (UO
  ₂), which was then reacted with carbon tetrachloride (CCl
  ₄) to produce uranium tetrachloride. Charles A. Kraus proposed a better method for large-scale production that involved reacting the uranium oxide with carbon tetrachloride at high temperature and pressure. This produced uranium pentachloride (UCl
  ₅) and phosgene (COCl
  ₂). While nowhere near as nasty as the uranium hexafluoride used by the gaseous diffusion process, uranium tetrachloride is hygroscopic, so work with it had to be undertaken in gloveboxes that were kept dry with phosphorus pentoxide (P
  ₄O
  ₁₀). The presence of phosgene, a lethal gas, required that the chemists wear gas masks when handling it.
  Of the $19.6 million spent on research and development of the electromagnetic process, $18 million (92 percent) was spent at the Radiation Laboratory in Berkeley, and further work conducted at Brown University, Johns Hopkins University and Purdue University, and by the Tennessee Eastman corporation. During 1943, the emphasis shifted from research to development, engin
caption: The XAX development unit at Oak Ridge was used for research, development and training.
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